Hi Sue, you have to use the Rapport with the ring - it doesn't work properly otherwise. But if you are intending on exercise rather than sex, your partner should try with the biggest size of ring to begin with. To use for penetrative sex, you opt for the smallest size ring he can bear but it might take some time and practice to get to that stage.
For exercise, pump slowly until it is nearly not comfortable, remove the pump and pull the sides of the ring to release the erection. Then start again. Ideal would be to repeat that 3 - 5 times, three times a day but with the Rapport this is a bit of a faff so once or twice, three times a day may be more achievable. Not so important to trim his pubic hair as with the other makes of pump but make sure he uses lots of lube on his penis and up the insides of the tube. KY jelly is probably cheapest & safest.